Add the Pharo language and IDE package

http://pharo.org

I'm one of the developers of Pharo and the creator and maintainer of the
Ubuntu PPA : https://launchpad.net/~pharo/+archive/stable.
It's better to use `callPackage_i686` instead. So just list the dependencies normally, and write
```
pharo-vm = callPackage_i686 ../development/pharo/vm { };
```
in `all-packages.nix`.